1. Field of the Invention
The invention relates to slag.
2. Prior Art
It is generally known to convert iron products obtained from a blast furnace into steel in a converter, for example by blowing through oxygen. During this treatment a steel slag is formed which, however, has various disadvantages which impede the use in practice.
Firstly, mention may be made of the particularly high content of free calcium oxide, as a result of which, when this slag is processed in road building materials, cracks can form in a road surface when the calcium oxide is converted into calcium hydroxide. This consequently leads to accelerated deterioration of a road surface made using such a slag.
Another disadvantage is the high weight per unit volume of 2,000 kg/m.sup.3.
Finally, this slag is difficult to process after solidification, since it must first be broken and screened in order to obtain usable particles of from 0 to 25 mm in size.
For all of these reasons there has been insufficient interest in steel slag hitherto. Heretofore, virtually the only known made for processing such steel slag was by mixing it with blast furnace slag and granulated blast furnace slag, 20% steel slag and 10% granulated blast furnace slag.
However, as a result of increasing processing of blast furnace slag in the cement industry, a much smaller amount of blast furnace slag is available for processing into a road building composition. As a result of this it is imperative to search for other applications for very large amounts of steel slag.
By way of illustration it may be mentioned that in the case of a relatively large processing unit for the conversion of pig iron into steel, about 450,000 tons of steel slag comprising about 300,000 tons of steel slag having a particle size of less than 25 mm becomes available. The coarser fraction, mainly measuring 40-180 mm, may be used in the hydraulic architecture. From the finer fraction only a minor amount thereof can be processed to road building material products by mixing it with blast furnace slag and granulated blast furnace slag, or it may be used as a gravel replacement in concrete and asphalt.
Heretofore, the finer fraction was used in the past as an agricultural fertilizer because of its high phosphorous content. Because of the use of richer iron ores, the phosphorous content has nevertheless been lowered. Further, the dispersion of the present heavy metals in the slag must be restricted in view of environmental measures. As yet there are no uses for the remainder of the slag.